Fetal Adaptation-Marks Flashcards
What is the oxygen saturation of a fetus?
About 70%
What are the 2 fetal adaptations to hypoxia?
- Hematological-fetal hemoglobin (HbF), 2. Cardiovascular-fetal circulation, brain and heart and organs that need blood most get it.
What are the hematological values of fetal hemoglobin relative to adult Hb?
More hemoglobin, higher hematocrit, higher mean corpuscular volume-bigger and newer red blood cells.
What is the polypeptide composition of HbF and HbA and when do they develop?
HbF is 2 alpha, 2 gamma, adult is 2 alpha, 2 beta. Gamma and alpha develop in the last few months before birth, beta develops at birth when oxygen rises. Differentation by primitive vs mature BFU.
Oxygen dissociation curve for fetal hemoglobin
Shifts up and to the left so that higher O2 sat for the same pO2.
What does the ductus venosus do?
Transfers from oxygenated umbilical vein and shunts away from liver circulation into IVC (left side-via dextra goes to LA), tunnels it. IVC is also getting blood from lower body (more on right side-via dextra goes to RV). Dilates if large hypoxia, by catecholamines.
Where does fetal blood go after leaving the LV?
Leaves ascending aorta into carotid arteries and into brain and into coronary artery. Will get to places that need the most oxygen.
How can we test for shunting through the ductus arteriosus after birth?
Saturation probe on right hand will be higher than left leg.
How do prostaglandins affect the ductus arteriosus?
Keep it open.
Why would you want to keep the ductus arteriosus open?
Anything that blood can’t get to lungs: pulmonary atresia, pulmonary hypertension, transposition of great vessels. Shunt will be L-R not R-L but will be useful.
What are signs of a fetus in hypoxic distress?
Bradycardia, deecreased movement, small body with large head, low level in amniotic fluid from renal failure, necrotising enterocolitis, increased hormones.
What are the organs that are least compromised (more privileged) during hypoxia?
Brain, adrenal glands, heart
What are the main changes at birth to alter hypoxic state?
Increased oxygenation in lungs, increased pH, decreased pulmonary vascular resistance and increased pulmonary blood flow.
Why did the pulmonary vascular resistance decrease?
- Oxygenation, release of vasodilators (NO from oxygenation), 2. Less acidosis (if acidosis maintained, PVR will be higher with same PO2, could be respiratory or vascular problem). 3. Fall in lung volume with air replacing water (alveolar squeezed out in vaginal air, chemical signals).
